Connection leasing for hosted services

ABSTRACT

Aspects herein describe techniques for brokering hosted resources in a virtual desktop infrastructure (VDI) using connection leases to reduce demand on connection brokers and to allow hosted services to be maintained even in the event of a broker outage. When a client device desires to connect to a hosted resource (e.g., a hosted desktop or a hosted application), the client device may present a lease token to the session host. The lease token is a self-sustaining package of data from which a session host can determine whether the requesting client device is authorized to access one or more resources hosted by that session host. The lease token may be cryptographically signed to ensure its contents have not been altered, and further that the lease token originated from a trusted source. Lease tokens may be stored independently from a connection broker, thereby still being usable if the connection broker goes offline.

CROSS-REFERENCE TO RELATED CASES

This application is a divisional application of Ser. No. 13/398,008,filed Feb. 16, 2012, having the title “Connection Leasing for HostedServices.”

FIELD

Aspects described herein relate to computer systems, computer networks,and desktop virtualization. More specifically, aspects described hereinrelate to the use of connection leases in desktop virtualization systemsto provide connectivity to remote desktops and remote applications by aclient device.

BACKGROUND

Traditionally, personal computers include combinations of operatingsystems, applications, and user settings, which are each managedindividually by owners or administrators on an ongoing basis. However,many organizations are now using desktop virtualization to provide amore flexible option to address the varying needs of their users. Indesktop virtualization, a user's computing environment (e.g., operatingsystem, applications, and/or user settings) may be separated from theuser's physical computing device (e.g., smartphone, laptop, desktopcomputer). Using client-server technology, a “virtualized desktop” maybe stored in and administered by a remote server, rather than in thelocal storage of the client computing device.

There are several different types of desktop virtualization systems. Asan example, Virtual Desktop Infrastructure (VDI) refers to the processof running a user desktop inside a virtual machine that resides on aserver. VDI and other server-based desktop virtualization systems mayprovide personalized desktops for each user, while allowing forcentralized management and security. Servers in such systems may includestorage for virtual desktop images and system configuration information,as well as software components to provide the virtual desktops and allowusers to interconnect to them. For example, a VDI server may include oneor more hypervisors (virtual machine managers) to create and maintainmultiple virtual machines, software to manage the hypervisor(s), aconnection broker, and software to provision and manage the virtualdesktops.

Desktop virtualization systems may be implemented using a singlevirtualization server or a combination of servers interconnected as aserver grid. Multi-server desktop virtualization systems often includeadditional computing devices and/or shared storage to provide a commonsystem management portal and to maintain global state information. Suchsystems often use the external shared storage, along with database andenterprise server software within the virtualization servers, to managethe system.

When a user desires to connect to a virtual desktop, the user's localsoftware client contacts a connection broker to establish a session witha remote desktop or other resource. Conventional connection brokers aresaid to be “inline” and thus involved in all decisions to determinewhere to direct a user's session. Stated differently, all connectionsmust be initiated through and established with the assistance of theconnection broker. As a result, the connection broker is a criticalpiece of infrastructure because an outage of the broker infrastructurewill result in a large-scale deployment outage, i.e., users will not beable to connect with hosted resources.

SUMMARY

In light of the foregoing background, the following presents asimplified summary of the present disclosure in order to provide a basicunderstanding of some aspects described herein. This summary is not anextensive overview, and is not intended to identify key or criticalelements or to delineate the scope of the claims. The following summarymerely presents various described aspects in a simplified form as aprelude to the more detailed description provided below.

In order to address the above shortcomings and additional benefits thatwill be realized upon reading the disclosure, aspects herein describenew methods and systems of brokering by using “connection leases” thatallow service to be maintained even in the event of a broker outage.According to some aspects, connection leases also serve to reduce theload placed on brokering infrastructure, thereby enabling higher-scaledeployments.

According to a first aspect, a lease token data structure may be used todefine a self-sustaining lease token. The data structure may include afirst data field identifying a lease token identification number, asecond data field identifying one or more client devices, a third datafield identifying one or more session hosts accessible by the one ormore client devices, and a fourth data field identifying one or moreresources usable by the one or more client devices on the one or moresession hosts, wherein each resource is one of a hosted desktop and ahosted application. The data structure may further include a fifth datafield identifying a connection limit constraining when the one or moreclient devices can access the one or more session hosts, a sixth datafield identifying one or more access conditions that must be met by theone or more client devices in order to access the one or more sessionhosts, a seventh data field identifying virtual channel informationusable by the one or more session hosts to allow or deny access by theone or more clients to one or more virtual channels on the one or moresession hosts, and an eighth data field storing a signature usable bythe one or more session hosts to verify that the lease token datastructure is unaltered and originated from a trusted connection broker.

According to another aspect, a session host apparatus may include aprocessor controlling operations of the session host apparatus, andmemory storing computer readable instructions that, when executed by theprocessor, cause the session host apparatus to establish a session witha session client using a connection lease. The session host receives alease token associated with a session client, where the lease token is aself-sustaining package of data from which the session host apparatuscan determine whether the session client device is authorized to accessone or more resources hosted by that session host. The session hostapparatus determines, based on the lease token, one or more resources,hosted by the session host apparatus, that the session client isauthorized to access. The session host apparatus sends connectioninformation to the session client based on the determined resources,after determining that the session client is authorized to access theone or more resources, and the session host apparatus then establishes asession with the session client to provide access to the one or moredetermined resources.

Yet another aspect described herein provides a method for establishing asession using a connection lease. Initially, a connection brokerreceives a request for a session from a client device. The connectionbroker determines, based on an identification of the client device, oneor more session hosts the client device is authorized to access, and oneor more resources the client device is authorized to use on the one ormore session hosts. The connection broker then generates a lease tokenbased on the client device, the one or more session hosts, and the oneor more resources, where the lease token is a self-sustaining package ofdata from which each of the one or more session hosts can determinewhether the client device is authorized to access the one or moreresources hosted by that session host. The connection broker sends thelease token for storage in a lease store. A session host receives thelease token as a request to establish a session with the client device,and the session host validates the lease token. Based on the validating,the session host sends connection information for use by the clientdevice to establish a session with the session host, and establishes thesession between the session host and the client device through which theclient device accesses one or more resources hosted by the session host.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described aspects of the disclosure in general terms,reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 illustrates an example operating environment in which variousaspects of the disclosure may be implemented.

FIG. 2 illustrates a client device that may be used in accordance withone or more illustrative aspects described herein.

FIG. 3 illustrates a client device that may be used in accordance withone or more illustrative aspects described herein.

FIG. 4 illustrates a system architecture in accordance with one or moreillustrative aspects described herein.

FIG. 5 illustrates data that may be included in a lease token, accordingto one or more illustrated aspects described herein.

FIG. 6 illustrates a data flow diagram for a method using connectionleases with a legacy session client, according to one or moreillustrated aspects described herein.

FIG. 7 illustrates a data flow diagram for a method using connectionleases by a lease-aware session client, according to one or moreillustrated aspects described herein.

DETAILED DESCRIPTION

In the following description of the various embodiments, reference ismade to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration various embodiments in whichaspects described herein may be practiced. It is to be understood thatother embodiments may be utilized and structural and functionalmodifications may be made without departing from the scope and spirit ofthe present disclosure.

As will be appreciated by one of skill in the art upon reading thefollowing disclosure, various aspects described herein may be embodiedas a method, a data processing system, or a computer program product.Accordingly, those aspects may take the form of an entirely hardwareembodiment, an entirely software embodiment or an embodiment combiningsoftware and hardware aspects. Furthermore, such aspects may take theform of a computer program product stored by one or morecomputer-readable storage media having computer-readable program code,or instructions, embodied in or on the storage media. Any suitablecomputer readable storage media may be utilized, including hard disks,CD-ROMs, optical storage devices, magnetic storage devices, and/or anycombination thereof. In addition, various signals representing data orevents as described herein may be transferred between a source and adestination in the form of electromagnetic waves traveling throughsignal-conducting media such as metal wires, optical fibers, and/orwireless transmission media (e.g., air and/or space).

FIG. 1 illustrates an example block diagram of a generic computingdevice 101 (e.g., a computer server 106 a) in an example computingenvironment 100 that may be used according to one or more illustrativeembodiments of the disclosure. According to one or more aspects, genericcomputing device 101 may be a server 106 a in a single-server ormulti-server desktop virtualization system configured to provide virtualmachines for client access devices. The generic computing device 101 mayhave a processor 103 for controlling overall operation of the server andits associated components, including random access memory (RAM) 105,read-only memory (ROM) 107, input/output (I/O) module 109, and memory115.

I/O module 109 may include a mouse, keypad, touch screen, scanner,optical reader, and/or stylus (or other input device(s)) through which auser of generic computing device 101 may provide input, and may alsoinclude one or more of a speaker for providing audio output and a videodisplay device for providing textual, audiovisual, and/or graphicaloutput. Software may be stored within memory 115 and/or other storage toprovide instructions to processor 103 for enabling generic computingdevice 101 to perform various functions. For example, memory 115 maystore software used by the generic computing device 101, such as anoperating system 117, application programs 119, and an associateddatabase 121. Alternatively, some or all of the computer executableinstructions for generic computing device 101 may be embodied inhardware or firmware (not shown).

The generic computing device 101 may operate in a networked environmentsupporting connections to one or more remote computers, such asterminals 140 (also referred to as client devices). The terminals 140may be personal computers or servers that include many or all of theelements described above with respect to the generic computing device101. The network connections depicted in FIG. 1 include a local areanetwork (LAN) 125 and a wide area network (WAN) 129, but may alsoinclude other networks. When used in a LAN networking environment, thegeneric computing device 101 may be connected to the LAN 125 through anetwork interface or adapter 123. When used in a WAN networkingenvironment, the generic computing device 101 may include a modem 127 orother network interface for establishing communications over the WAN129, such as computer network 130 (e.g., the Internet). It will beappreciated that the network connections shown are illustrative andother means of establishing a communications link between the computersmay be used.

Generic computing device 101 and/or terminals 140 may also be mobileterminals (e.g., mobile phones, smartphones, PDAs, notebooks, etc.)including various other components, such as a battery, speaker, andantennas (not shown).

The disclosure is operational with numerous other general purpose orspecial purpose computing system environments or configurations.Examples of well-known computing systems, environments, and/orconfigurations that may be suitable for use with the disclosure include,but are not limited to, personal computers, server computers, hand-heldor laptop devices, multiprocessor systems, microprocessor-based systems,set top boxes, programmable consumer electronics, network PCs,minicomputers, mainframe computers, distributed computing environmentsthat include any of the above systems or devices, and the like.

As shown in FIG. 1, one or more client devices 140 may be incommunication with one or more servers 106 a-106 n (generally referredto herein as “server(s) 106”). In one embodiment, the computingenvironment 100 can include an appliance installed between the server(s)106 and client machine(s) 140. This appliance can manage client/serverconnections, and in some cases can load balance client connectionsamongst a plurality of backend servers 106.

The client machine(s) 140 can in some embodiment be referred to as asingle client machine 140 or a single group of client machines 140,while server(s) 106 may be referred to as a single server 106 or asingle group of servers 106. In one embodiment a single client machine140 communicates with more than one server 106, while in anotherembodiment a single server 106 communicates with more than one clientmachine 140. In yet another embodiment, a single client machine 140communicates with a single server 106.

A client machine 140 can, in some embodiments, be referenced by any oneof the following terms: client machine(s) 140; client(s); clientcomputer(s); client device(s); client computing device(s); localmachine; remote machine; client node(s); endpoint(s); endpoint node(s);or a second machine. The server 106, in some embodiments, may bereferenced by any one of the following terms: server(s), local machine;remote machine; server farm(s), host computing device(s), or a firstmachine(s).

In one embodiment, the client machine 140 may be a virtual machine. Thevirtual machine may be any virtual machine, while in some embodimentsthe virtual machine may be any virtual machine managed by a hypervisordeveloped by Citrix Systems, IBM, VMware, or any other hypervisor. Insome aspects, the virtual machine may be managed by a hypervisor, whilein aspects the virtual machine may be managed by a hypervisor executingon a server 106 or a hypervisor executing on a client 140.

The client machine 140 may execute, operate or otherwise provide anapplication that can be any one of the following: software; a program;executable instructions; a virtual machine; a hypervisor; a web browser;a web-based client; a client-server application; a thin-client computingclient; an ActiveX control; a Java applet; software related to voiceover internet protocol (VoIP) communications like a soft IP telephone;an application for streaming video and/or audio; an application forfacilitating real-time-data communications; a HTTP client; a FTP client;an Oscar client; a Telnet client; or any other set of executableinstructions. Still other embodiments include a client device 140 thatdisplays application output generated by an application remotelyexecuting on a server 106 or other remotely located machine. In theseembodiments, the client device 140 can display the application output inan application window, a browser, or other output window. In oneexample, the application is a desktop, while in other examples theapplication is an application that generates a desktop. A desktop mayinclude a graphical shell providing a user interface for an instance ofan operating system in which local and/or remote applications can beintegrated. Applications, as used herein, are programs that executeafter an instance of an operating system (and, optionally, also thedesktop) has been loaded.

The server 106, in some embodiments, executes a remote presentationclient or other client or program that uses a thin-client orremote-display protocol to capture display output generated by anapplication executing on a server 106 and transmits the applicationdisplay output to a remote client 140. The thin-client or remote-displayprotocol can be any one of the following protocols: the IndependentComputing Architecture (ICA) protocol manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla.; or the Remote Desktop Protocol (RDP)manufactured by the Microsoft Corporation of Redmond, Wash.

The computing environment can include more than one server 106A-106Nsuch that the servers 106A-106N are logically grouped together into aserver farm 106. The server farm 106 can include servers 106 that aregeographically dispersed and logically grouped together in a server farm106, or servers 106 that are located proximate to each other andlogically grouped together in a server farm 106. Geographicallydispersed servers 106A-106N within a server farm 106 can, in someembodiments, communicate using a WAN, MAN, or LAN, where differentgeographic regions can be characterized as: different continents;different regions of a continent; different countries; different states;different cities; different campuses; different rooms; or anycombination of the preceding geographical locations. In some embodimentsthe server farm 106 may be administered as a single entity, while inother embodiments the server farm 106 can include multiple server farms106.

In some embodiments, a server farm 106 can include servers 106 thatexecute a substantially similar type of operating system platform (e.g.,Windows Server, manufactured by Microsoft Corp. of Redmond, Wash., UNIX,LINUX, iOS, or LION, etc.) In other embodiments, the server farm 106 caninclude a first group of servers 106 that execute a first type ofoperating system platform, and a second group of servers 106 thatexecute a second type of operating system platform. The server farm 106,in other embodiments, can include servers 106 that execute differenttypes of operating system platforms.

The server 106, in some embodiments, can be any server type. In otherembodiments, the server 106 can be any of the following server types: afile server; an application server; a web server; a proxy server; anappliance; a network appliance; a gateway; an application gateway; agateway server; a virtualization server; a deployment server; a SSL VPNserver; a firewall; a web server; an application server or as a masterapplication server; a server 106 executing an active directory; or aserver 106 executing an application acceleration program that providesfirewall functionality, application functionality, or load balancingfunctionality. In some embodiments, a server 106 may be a RADIUS serverthat includes a remote authentication dial-in user service. Inembodiments where the server 106 comprises an appliance, the server 106can be an appliance manufactured by any one of the followingmanufacturers: the Citrix Application Networking Group; Silver PeakSystems, Inc.; Riverbed Technology, Inc.; F5 Networks, Inc.; or JuniperNetworks, Inc. Some embodiments include a first server 106A thatreceives requests from a client machine 140, forwards the request to asecond server 106 n, and responds to the request generated by the clientmachine 140 with a response from the second server 106 n. The firstserver 106A can acquire an enumeration of applications available to theclient machine 140 and well as address information associated with anapplication server 106 hosting an application identified within theenumeration of applications. The first server 106A can then present aresponse to the client's request using a web interface, and communicatedirectly with the client 140 to provide the client 140 with access to anidentified application.

The server 106 can, in some embodiments, execute any one of thefollowing applications: a thin-client application using a thin-clientprotocol to transmit application display data to a client; a remotedisplay presentation application; any portion of the CITRIX ACCESS SUITEby Citrix Systems, Inc. like XENAPP, XENDESKTOP, METAFRAME or CITRIXPRESENTATION SERVER; MICROSOFT WINDOWS Terminal Services manufactured bythe Microsoft Corporation; or an ICA client, developed by CitrixSystems, Inc. Another embodiment includes a server 106 that is anapplication server such as: an email server that provides email servicessuch as MICROSOFT EXCHANGE manufactured by the Microsoft Corporation; aweb or Internet server; a desktop sharing server; a collaborationserver; or any other type of application server. Still other embodimentsinclude a server 106 that executes any one of the following types ofhosted servers applications: GOTOMEETING provided by Citrix OnlineDivision, Inc.; WEBEX provided by WebEx, Inc. of Santa Clara, Calif.; orMicrosoft Office LIVE MEETING provided by Microsoft Corporation.

Client machines 140 can, in some embodiments, be a client node thatseeks access to resources provided by a server 106. In otherembodiments, the server 106 may provide clients 140 or client nodes withaccess to hosted resources. The server 106, in some embodiments,functions as a master node such that it communicates with one or moreclients 140 or servers 106. In some embodiments, the master node canidentify and provide address information associated with a server 106hosting a requested application, to one or more clients 140 or servers106. In still other embodiments, the master node can be a server farm106, a client 140, a cluster of client nodes 140, or an appliance.

One or more clients 140 and/or one or more servers 106 can transmit dataover a network 130 installed between machines and appliances within thecomputing environment 100. The network 130 can comprise one or moresub-networks, and can be installed between any combination of theclients 140, servers 106, computing machines and appliances includedwithin the computing environment 100. In some embodiments, the network130 can be: a local-area network (LAN); a metropolitan area network(MAN); a wide area network (WAN); a primary network 104 comprised ofmultiple sub-networks located between the client machines 140 and theservers 106; a primary public network 130 (e.g., the Internet) with aprivate sub-network; a primary private network 130 with a publicsub-network; or a primary private network 130 with a privatesub-network. Still further embodiments include a network 130 that can beany of the following network types: a point to point network; abroadcast network; a telecommunications network; a data communicationnetwork; a computer network; an ATM (Asynchronous Transfer Mode)network; a SONET (Synchronous Optical Network) network; a SDH(Synchronous Digital Hierarchy) network; a wireless network; a wirelinenetwork; or a network that includes a wireless link where the wirelesslink can be an infrared channel or satellite band. The network topologyof the network 130 can differ within different embodiments, possiblenetwork topologies include: a bus network topology; a star networktopology; a ring network topology; a repeater-based network topology; ora tiered-star network topology. Additional embodiments may include anetwork of mobile telephone networks that use a protocol to communicateamong mobile devices, where the protocol can be any one of thefollowing: AMPS; TDMA; CDMA; GSM; GPRS UMTS; or any other protocol ableto transmit data among mobile devices.

Illustrated in FIG. 2 is an embodiment of a computing device 200, wherethe client machine 140 and server 106 illustrated in FIG. 1 may bedeployed as and/or executed on any embodiment of the computing device200 illustrated and described herein. Included within the computingdevice 200 is a system bus 250 that communicates with the followingcomponents: a central processing unit 221; a main memory 222; storagememory 228; an input/output (I/O) controller 223; display devices224A-224N; an installation device 216; and a network interface 218. Inone embodiment, the storage memory 228 includes: an operating system,software routines, and a client agent 220. The I/O controller 223, insome embodiments, is further connected to a keyboard 226, and a pointingdevice 227. Other embodiments may include an I/O controller 223connected to more than one input/output device 230A-230N.

FIG. 3 illustrates one embodiment of a computing device 300, where theclient machine 140 and server 106 illustrated in FIG. 1 can be deployedas and/or executed on any embodiment of the computing device 300illustrated and described herein. Included within the computing device300 is a system bus 350 that communicates with the following components:a bridge 370, and a first I/O device 330 a. In another embodiment, thebridge 370 is in further communication with the main central processingunit 321, where the central processing unit 321 can further communicatewith a second I/O device 330 b, a main memory 322, and a cache memory340. Included within the central processing unit 321, are I/O ports, amemory port 303, and a main processor.

Embodiments of the computing machine 300 can include a centralprocessing unit 321 characterized by any one of the following componentconfigurations: logic circuits that respond to and process instructionsfetched from the main memory unit 322; a microprocessor unit, such as:those manufactured by Intel Corporation; those manufactured by MotorolaCorporation; those manufactured by Transmeta Corporation of Santa Clara,Calif.; the RS/6000 processor such as those manufactured byInternational Business Machines; a processor such as those manufacturedby Advanced Micro Devices; or any other combination of logic circuits.Still other embodiments of the central processing unit 322 may includeany combination of the following: a microprocessor, a microcontroller, acentral processing unit with a single processing core, a centralprocessing unit with two processing cores, or a central processing unitwith more than one processing core.

While FIG. 3 illustrates a computing device 300 that includes a singlecentral processing unit 321, in some embodiments the computing device300 can include one or more processing units 321. In these embodiments,the computing device 300 may store and execute firmware or otherexecutable instructions that, when executed, direct the one or moreprocessing units 321 to simultaneously execute instructions or tosimultaneously execute instructions on a single piece of data. In otherembodiments, the computing device 300 may store and execute firmware orother executable instructions that, when executed, direct the one ormore processing units to each execute a section of a group ofinstructions. For example, each processing unit 321 may be instructed toexecute a portion of a program or a particular module within a program.

In some embodiments, the processing unit 321 can include one or moreprocessing cores. For example, the processing unit 321 may have twocores, four cores, eight cores, etc. In one embodiment, the processingunit 321 may comprise one or more parallel processing cores. Theprocessing cores of the processing unit 321, may in some embodimentsaccess available memory as a global address space, or in otherembodiments, memory within the computing device 300 can be segmented andassigned to a particular core within the processing unit 321. In oneembodiment, the one or more processing cores or processors in thecomputing device 300 can each access local memory. In still anotherembodiment, memory within the computing device 300 can be shared amongstone or more processors or processing cores, while other memory can beaccessed by particular processors or subsets of processors. Inembodiments where the computing device 300 includes more than oneprocessing unit, the multiple processing units can be included in asingle integrated circuit (IC). These multiple processors, in someembodiments, can be linked together by an internal high speed bus, whichmay be referred to as an element interconnect bus.

In embodiments where the computing device 300 includes one or moreprocessing units 321, or a processing unit 321 including one or moreprocessing cores, the processors can execute a single instructionsimultaneously on multiple pieces of data (SIMD), or in otherembodiments can execute multiple instructions simultaneously on multiplepieces of data (MIMD). In some embodiments, the computing device 100 caninclude any number of SIMD and MIMD processors.

The computing device 300, in some embodiments, can include a graphicsprocessor or a graphics processing unit (Not Shown). The graphicsprocessing unit can include any combination of software and hardware,and can further input graphics data and graphics instructions, render agraphic from the inputted data and instructions, and output the renderedgraphic. In some embodiments, the graphics processing unit can beincluded within the processing unit 321. In other embodiments, thecomputing device 300 can include one or more processing units 321, whereat least one processing unit 321 is dedicated to processing andrendering graphics.

One embodiment of the computing machine 300 includes a centralprocessing unit 321 that communicates with cache memory 340 via asecondary bus also known as a backside bus, while another embodiment ofthe computing machine 300 includes a central processing unit 321 thatcommunicates with cache memory via the system bus 350. The local systembus 350 can, in some embodiments, also be used by the central processingunit to communicate with more than one type of I/O device 330 a-330 n.In some embodiments, the local system bus 350 can be any one of thefollowing types of buses: a VESA VL bus; an ISA bus; an EISA bus; aMicroChannel Architecture (MCA) bus; a PCI bus; a PCI-X bus; aPCI-Express bus; or a NuBus. Other embodiments of the computing machine300 include an I/O device 330 a-330 n that includes a video display 224that communicates with the central processing unit 321. Still otherversions of the computing machine 300 include a processor 321 connectedto an I/O device 330 a-330 n via any one of the following connections:HyperTransport, Rapid I/O, or InfiniBand. Further embodiments of thecomputing machine 300 include a processor 321 that communicates with oneI/O device 330 a using a local interconnect bus and a second I/O device330 b using a direct connection.

The computing device 300, in some embodiments, includes a main memoryunit 322 and cache memory 340. The cache memory 340 can be any memorytype, and in some embodiments can be any one of the following types ofmemory: SRAM; BSRAM; or EDRAM. Other embodiments include cache memory340 and a main memory unit 322 that can be any one of the followingtypes of memory: Static random access memory (SRAM), Burst SRAM orSynchBurst SRAM (BSRAM); Dynamic random access memory (DRAM); Fast PageMode DRAM (FPM DRAM); Enhanced DRAM (EDRAM), Extended Data Output RAM(EDO RAM); Extended Data Output DRAM (EDO DRAM); Burst Extended DataOutput DRAM (BEDO DRAM); Enhanced DRAM (EDRAM); synchronous DRAM(SDRAM); JEDEC SRAM; PC100 SDRAM; Double Data Rate SDRAM (DDR SDRAM);Enhanced SDRAM (ESDRAM); SyncLink DRAM (SLDRAM); Direct Rambus DRAM(DRDRAM); Ferroelectric RAM (FRAM); or any other type of memory. Furtherembodiments include a central processing unit 321 that can access themain memory 322 via: a system bus 350; a memory port 303; or any otherconnection, bus or port that allows the processor 321 to access memory322.

One embodiment of the computing device 200/300 provides support for anyone of the following installation devices 216: a CD-ROM drive, a CD-R/RWdrive, a DVD-ROM drive, tape drives of various formats, USB device, abootable medium, a bootable CD, a bootable CD for GNU/Linux distributionsuch as KNOPPIX®, a hard-drive or any other device suitable forinstalling applications or software. Applications can in someembodiments include a client agent 220, or any portion of a client agent220. The computing device 200/300 may further include a storage device228 that can be either one or more hard disk drives, or one or moreredundant arrays of independent disks; where the storage device isconfigured to store an operating system, software, programsapplications, or at least a portion of the client agent 220. A furtherembodiment of the computing device 200, 300 includes an installationdevice 216 that is used as the storage device 228.

The computing device 200, 300 may further include a network interface218 to interface to a Local Area Network (LAN), Wide Area Network (WAN)or the Internet through a variety of connections including, but notlimited to, standard telephone lines, LAN or WAN links (e.g., 802.11,T1, T3, 56kb, X.25, SNA, DECNET), broadband connections (e.g., ISDN,Frame Relay, ATM, Gigabit Ethernet, Ethernet-over-SONET), wirelessconnections, or some combination of any or all of the above. Connectionscan also be established using a variety of communication protocols(e.g., TCP/IP, IPX, SPX, NetBIOS, Ethernet, ARCNET, SONET, SDH, FiberDistributed Data Interface (FDDI), RS232, RS485, IEEE 802.11, IEEE802.11a, IEEE 802.11b, IEEE 802.11g, CDMA, GSM, WiMax and directasynchronous connections). One version of the computing device 200, 300includes a network interface 218 able to communicate with additionalcomputing devices 200′, 300′ via any type and/or form of gateway ortunneling protocol such as Secure Socket Layer (SSL) or Transport LayerSecurity (TLS), or the Citrix Gateway Protocol manufactured by CitrixSystems, Inc. Versions of the network interface 218 can comprise any oneof: a built-in network adapter; a network interface card; a PCMCIAnetwork card; a card bus network adapter; a wireless network adapter; aUSB network adapter; a modem; or any other device suitable forinterfacing the computing device 200, 300 to a network capable ofcommunicating and performing the methods and systems described herein.

Embodiments of the computing device 200, 300 include any one of thefollowing I/O devices 230 a-230 n: a keyboard 226; a pointing device227; mice; trackpads; an optical pen; trackballs; microphones; drawingtablets; video displays; speakers; inkjet printers; laser printers; anddye-sublimation printers; or any other input/output device able toperform the methods and systems described herein. An I/O controller 223may in some embodiments connect to multiple I/O devices 230 a-230 n tocontrol the one or more I/O devices. Some embodiments of the I/O devices230 a-230 n may be configured to provide storage or an installationmedium 216, while others may provide a universal serial bus (USB)interface for receiving USB storage devices such as the USB Flash Driveline of devices manufactured by Twintech Industry, Inc. Still otherembodiments include an I/O device 230 that may be a bridge between thesystem bus 250 and an external communication bus, such as: a USB bus; anApple Desktop Bus; an RS-232 serial connection; a SCSI bus; a FireWirebus; a FireWire 800 bus; an Ethernet bus; an AppleTalk bus; a GigabitEthernet bus; an Asynchronous Transfer Mode bus; a HIPPI bus; a SuperHIPPI bus; a SerialPlus bus; a SCl/LAMP bus; a FibreChannel bus; or aSerial Attached small computer system interface bus.

In some embodiments, the computing machine 200, 300 can connect tomultiple display devices 224 a-224 n, in other embodiments the computingdevice 100 can connect to a single display device 224, while in stillother embodiments the computing device 200, 300 connects to displaydevices 224 a-224 n that are the same type or form of display, or todisplay devices that are different types or forms. Embodiments of thedisplay devices 224 a-224 n can be supported and enabled by thefollowing: one or multiple I/O devices 230 a-230 n; the I/O controller223; a combination of I/O device(s) 230 a-230 n and the I/O controller223; any combination of hardware and software able to support a displaydevice 224 a-224 n; any type and/or form of video adapter, video card,driver, and/or library to interface, communicate, connect or otherwiseuse the display devices 224 a-224 n. The computing device 200, 300 mayin some embodiments be configured to use one or multiple display devices224A-224N, these configurations include: having multiple connectors tointerface to multiple display devices 224A-224N; having multiple videoadapters, with each video adapter connected to one or more of thedisplay devices 224A-224N; having an operating system configured tosupport multiple displays 224A-224N; using circuits and softwareincluded within the computing device 200 to connect to and use multipledisplay devices 224A-224N; and executing software on the main computingdevice 200 and multiple secondary computing devices to enable the maincomputing device 200 to use a secondary computing device's display as adisplay device 224A-224N for the main computing device 200. Still otherembodiments of the computing device 200 may include multiple displaydevices 224A-224N provided by multiple secondary computing devices andconnected to the main computing device 200 via a network.

In some embodiments, the computing machine 200 can execute any operatingsystem, while in other embodiments the computing machine 200 can executeany of the following operating systems: versions of the MICROSOFTWINDOWS operating systems such as WINDOWS 3.x; WINDOWS 95; WINDOWS 98;WINDOWS 2000; WINDOWS NT 3.51; WINDOWS NT 4.0; WINDOWS CE; WINDOWS XP;WINDOWS VISTA, WINDOWS 7, WINDOWS SERVER, and the like; the differentreleases of the Unix and Linux operating systems; any version of the MACOS manufactured by Apple Computer; OS/2, manufactured by InternationalBusiness Machines; any embedded operating system; any real-timeoperating system; any open source operating system; any proprietaryoperating system; any operating systems for mobile computing devices; orany other operating system. In still another embodiment, the computingmachine 200 can execute multiple operating systems. For example, thecomputing machine 200 can execute PARALLELS or another virtualizationplatform that can execute or manage a virtual machine executing a firstoperating system, while the computing machine 200 executes a secondoperating system different from the first operating system.

The computing machine 200 can be embodied in any one of the followingcomputing devices: a computing workstation; a desktop computer; a laptopor notebook computer; a server; a handheld computer; a mobile telephone;a portable telecommunication device; a media playing device; a gamingsystem; a mobile computing device; a netbook; a device of the IPODfamily of devices manufactured by Apple Computer; any one of thePLAYSTATION family of devices manufactured by the Sony Corporation; anyone of the Nintendo family of devices manufactured by Nintendo Co; anyone of the XBOX family of devices manufactured by the MicrosoftCorporation; or any other type and/or form of computing,telecommunications or media device that is capable of communication andthat has sufficient processor power and memory capacity to perform themethods and systems described herein. In other embodiments the computingmachine 100 can be a mobile device such as any one of the followingmobile devices: a JAVA-enabled cellular telephone or personal digitalassistant (PDA), such as the i55sr, i58sr, i85s, i88s, i90c, i95c1, orthe im1100, all of which are manufactured by Motorola Corp; the 6035 orthe 7135, manufactured by Kyocera; the i300 or i330, manufactured bySamsung Electronics Co., Ltd; the TREO 180, 270, 600, 650, 680, 700p,700w, or 750 smart phone manufactured by Palm, Inc; any computing devicethat has different processors, operating systems, and input devicesconsistent with the device; or any other mobile computing device capableof performing the methods and systems described herein. In still otherembodiments, the computing device 200 can be any one of the followingmobile computing devices: any one series of Blackberry, or otherhandheld device manufactured by Research In Motion Limited; the iPhonemanufactured by Apple Computer; Palm Pre; a Pocket PC; a Pocket PCPhone; or any other handheld mobile device.

In some embodiments, the computing device 200 may have differentprocessors, operating systems, and input devices consistent with thedevice. For example, in one embodiment, the computing device 200 is aTREO 180, 270, 600, 650, 680, 700p, 700w, or 750 smart phonemanufactured by Palm, Inc. In some of these embodiments, the TREO smartphone is operated under the control of the PalmOS operating system andincludes a stylus input device as well as a five-way navigator device.

In other embodiments the computing device 200 is a mobile device, suchas a JAVA-enabled cellular telephone or personal digital assistant(PDA), such as the i55sr, i58sr, i85s, i88s, i90c, i95c1, or the im1100,all of which are manufactured by Motorola Corp. of Schaumburg, Ill., the6035 or the 7135, manufactured by Kyocera of Kyoto, Japan, or the i300or i330, manufactured by Samsung Electronics Co., Ltd., of Seoul, Korea.In some embodiments, the computing device 200 is a mobile devicemanufactured by Nokia of Finland, or by Sony Ericsson MobileCommunications AB of Lund, Sweden.

In still other embodiments, the computing device 200 is a Blackberryhandheld or smart phone, such as the devices manufactured by Research InMotion Limited, including the Blackberry 7100 series, 8700 series, 7700series, 7200 series, the Blackberry 7520, or the Blackberry Pearl 8100.In yet other embodiments, the computing device 200 is a smart phone,Pocket PC, Pocket PC Phone, or other handheld mobile device supportingMicrosoft Windows Mobile Software. Moreover, the computing device 200can be any workstation, desktop computer, laptop or notebook computer,server, handheld computer, mobile telephone, any other computer, orother form of computing or telecommunications device that is capable ofcommunication and that has sufficient processor power and memorycapacity to perform the operations described herein.

In some embodiments, the computing device 200 is a digital audio player.In one of these embodiments, the computing device 200 is a digital audioplayer such as the Apple IPOD, IPOD Touch, IPOD NANO, and IPOD SHUFFLElines of devices, manufactured by Apple Computer of Cupertino, Calif. Inanother of these embodiments, the digital audio player may function asboth a portable media player and as a mass storage device. In otherembodiments, the computing device 200 is a digital audio player such asthe DigitalAudioPlayer Select MP3 players, manufactured by SamsungElectronics America, of Ridgefield Park, N.J., or the Motorola m500 orm25 Digital Audio Players, manufactured by Motorola Inc. of Schaumburg,Ill. In still other embodiments, the computing device 200 is a portablemedia player, such as the Zen Vision W, the Zen Vision series, the ZenPortable Media Center devices, or the Digital MP3 line of MP3 players,manufactured by Creative Technologies Ltd. In yet other embodiments, thecomputing device 200 is a portable media player or digital audio playersupporting file formats including, but not limited to, MP3, WAV,M4A/AAC, WMA Protected AAC, AIFF, Audible audiobook, Apple Losslessaudio file formats and .mov, .m4v, and .mp4 MPEG-4 (H.264/MPEG-4 AVC)video file formats.

In some embodiments, the computing device 200 comprises a combination ofdevices, such as a mobile phone combined with a digital audio player orportable media player. In one of these embodiments, the computing device200 is a Motorola RAZR or Motorola ROKR line of combination digitalaudio players and mobile phones. In another of these embodiments, thecomputing device 200 is an iPhone smartphone, manufactured by AppleComputer of Cupertino, Calif.

FIGS. 1-3 show a high-level architecture of an illustrative desktopvirtualization system. As shown, the desktop virtualization system maybe single-server or multi-server system, including at least onevirtualization server 106 configured to provide virtual desktops and/orvirtual applications to one or more client access devices 140. As usedherein, a desktop refers to a graphical environment or space in whichone or more applications may be hosted and/or executed. A desktop mayinclude a graphical shell providing a user interface for an instance ofan operating system in which local and/or remote applications can beintegrated. Applications, as used herein, are programs that executeafter an instance of an operating system (and, optionally, also thedesktop) has been loaded. Each instance of the operating system may bephysical (e.g., one operating system per device) or virtual (e.g., manyinstances of an OS running on a single device). Each application may beexecuted on a local device, or executed on a remotely located device(e.g., remoted).

Having described in FIGS. 1-3 various examples of desktop virtualizationsystems, and certain software and functionality that may be included inservers 106 of such systems, the following paragraphs provide additionalexamples of various methods and systems relating to using connectionleasing as a brokerage model for establishing user sessions with remoteresources.

Connection leasing is most effective in scenarios where a typical userconnects to a relatively small number of session hosts (virtual desktopsor remote desktop services (RDS) servers) from a relatively small numberof client devices, and that over time a brokering decision is stable,e.g., the brokering decision made yesterday is likely to be the samedecision made today, and will be the same decision made tomorrow. Whenbrokering decisions remain constant over time, it becomes an unnecessarywaste of resources to require a user to complete the entire inlinebrokering process each time the user desires to connect to a sessionhost, because the brokering decision will likely remain unchangedinsofar as the user is granted the same rights to the same or similarsession host(s). However, even in scenarios where brokerage decisionschange regularly, there are still benefits to be gained from using theleasing model described herein.

With reference to FIG. 4, one or more external client devices 405 a-405n may communicate with connection broker 430 via one or more networks415, 435. Network 415 may include a public network such as the Internet.Network 435 may include a private network such as a corporate LAN, WANor the like, protected by firewall 420. Any other networks may also beused.

External client device 405 may communicate through firewall 420 via anedge device 425, such as an access gateway, virtual private network(VPN) server, or the like. Web server 430 may include an externallyfacing aspect and an internally facing aspect for communicating withexternal client devices 405 and internal client devices 410,respectively. Alternatively, a single logical web server may be adaptedor configured to communicate with all client devices. Web server 430communicates with connection broker 401 to handle requests for sessionswith virtualized resources, as further described herein. In some aspectsweb server 430 and connection broker 401 are physically and/or logicallyseparate devices. In other aspects web server 430 and connection broker401 may be physically and/or logically combined.

Connection broker 401 may receive login credentials from users at clientdevices 405, 410 (e.g., via a web server 430 or other client-serverconfiguration), and then creates and/or assigns resources to authorizedusers, and provides management consoles to authorized administrators.Each resource, e.g., a hosted application, hosted resource, virtualmachine, or the like, may be hosted by one or more session hosts 440a-440 n.

With reference to FIG. 5, connection broker 401, acting as a leaseissuer, may issue a connection lease that can be used multiple times. Aconnection lease may be thought of as a static assignment of a clientdevice and/or user to a particular session host (or hosts) having aparticular set of resources. The lease may be defined by a lease token501 stored as a data package, e.g., in XML or other suitable format. Asused herein, a lease token is a self-sustaining package of data fromwhich a session host can determine whether a client device is authorizedto access one or more resources (e.g., applications, desktops, printingservices, audio services, virtual channels, etc.) hosted by that sessionhost, as well as whether the client device is authorized to exposeclient-side resources to the session host (e.g., attached peripherals,printer, etc., attached to client). The session client may needadditional information to complete session establishment, but thesession host can independently determine that the session client isauthorized without querying a connection broker (except as to possiblelease token revocation, as further discussed below).

The lease token defines the authorizations provided by a particularlease, and may be defined to be valid for some period of time, e.g., fora discrete number of connections 503 or for a specified duration of time505A, 505B. A lease token may include information 507 usable by a clientdevice (end-point device) to directly initiate a connection to aspecified set of session hosts, such as DNS or IP addresses. While thespecified set of session hosts 507 may typically be few in number, anyset of session hosts may be specified. Each lease token may furtherinclude identities of one or more resources 509 that the user may accesson the specified session hosts. The resources may include a desktopand/or individual applications. The connection lease may further specifyinformation necessary for the user to access the leased resources, e.g.,file paths to one or more authorized applications.

Each connection lease may be cryptographically signed 511 so that asession host can verify the validity of the lease without needing tocommunicate with a broker. For example, in a public key infrastructure(PKI), each connection lease might be signed and/or encrypted using aprivate key of the broker 401, and each session host can verify thelease by authenticating or decrypting the connection lease using thepublic key of the trusted broker. The session host can thereby ensurethat the information included in the lease is provided by a trustedbroker. The broker may further include a hash value associated with thelease token to ensure that the lease is not improperly altered orchanged after issuance by the broker and before use by a user or device.

According to some aspects, additional security may be included in leasetokens to prevent misuse. In one example, a lease may includeinformation that can be compared by the session host against theattributes of any requested connection, including but not limited to,the identity 513 of the user or of devices from which a connection canbe established (so that a stolen lease token cannot be misused), thevalidity period 505 of the lease token (so that a token cannot be usedindefinitely), one or more access conditions 515 (such as the clientdevice's anti-virus state, which may be determined by a network devicesuch as an Access Gateway), and access or logon hours.

According to yet other aspects, the lease token may also includeinformation usable by a session host to implement a security policy.Such information may include a maximum idle time 517 before automaticdisconnection, maximum disconnected time 519 before automatic logoff,and control of which devices may be used 521 (virtual channel control).Virtual channel control refers to the ability to control a printerchannel, video channel, audio channel, etc., during the virtualizedsession.

Once a broker issues a lease token, the tokens themselves may be storedon a client device (endpoint device) or other locations. By storing thelease token on the endpoint device, however, only the endpoint device,network and session host need to be available in order for a session tobe established. If a connection broker is unavailable, the session canstill be established provided the lease token remains valid. In anotherexample, the lease token may be stored on a network device or server,such as an access gateway, web interface, or other device located at theedge of the network. In yet other examples, lease tokens may be storedon the connection brokers themselves so that the brokers can continue tooffer service in the event of a database outage. In addition, each leasetoken may be stored in multiple locations for redundancy, e.g., on theendpoint device as well as on the connection broker. Because each leasetoken defines its parameters of acceptable use (e.g., permitted user,permitted user device(s), permitted sessions host(s), permittedconnections, permitted resources, etc.), there is no risk ofunauthorized use based on duplication of lease tokens.

With reference to FIG. 6, currently deployed virtualization softwareexpects to initiate a connection using a traditional inline connectionbroker, and thus may need to be adapted for use with the inventiveconnection lease system described herein. In order to establishbackwards compatibility with existing virtualization systems andsoftware, a lease store 602 and lease presenter 604 may be established.The lease store 602 is a central repository, or repositories, wherelease tokens may be stored. There may be more than one lease store 602in a given virtualization system, e.g., one lease store per leasepresenter, or some other amount. The lease presenter refers to asoftware service introduced between the session client and theconnection broker, that in effect intercepts a session client's requestto a connection broker, and determines whether there is already anexisting lease token for that session client. Lease presenter 604 mayreside, for example, at the edge of a network, or at a network gateway(e.g., in server 425), and may be replicated in multiple locationsaround the edge of the network. This is unlike the connection broker,which typically exists in only a single instance within eachvirtualization system.

Using the lease presenter 604 and lease store 602, a legacy sessionclient 608 may establish a session using lease tokens as follows. When auser desires to establish a connection with a session host 606, the userlogs in or presents authentication credentials and the session clientcalls the connection broker to obtain connection information, expectingto receive a typical ICA or RDP file. The lease presenter 604 interceptsthe call to the connection broker and, upon verifying the user and orclient's credentials, checks the lease store 602 for an existing leasetoken for that session client. If no lease token exists, or no leasetoken exists with suitable constraints (e.g., attempting to connectoutside of logon hours, or with a different client device), then thelease presenter may query the connection broker 401 for a new token forthe session client, and then in step 601 the lease token is stored inlease store 602.

In step 603, the lease presenter requests the lease token from the tokenstore, and in step 605, the lease token is provided to the leasepresenter. The lease presenter then presents the lease token to one ormore session hosts in step 607 as defined by the lease token. The leasepresenter may further provide confirmation to the session host that theuser has already been authenticated. Alternatively the lease token maybe delivered to the session host by a network device, virtual machine(VM) or other server such as an Access Gateway, Web Interface, DeliveryServices or the broker itself (any of which can act as the “leasepresenter”), after intercepting the initial request from the sessionclient. As part of “presenting” the lease, the lease presenter mayrequest one-time connection tickets, logon tickets, etc., or any otherinformation required to generate a typical launch file.

The session host(s) may verify the lease token, and further verify theuser's authenticity if needed. Each session host may represent oradminister multiple desktops, applications, and/or other hostedservices. Thus, in step 609 the session host determines which hostedservice the session client is to be connected to, and returns additionalconnection details to the lease presenter. The additional connectiondetails may include an IP address or DNS specific to the desktop orother hosted service, and any other information needed by the leasepresenter to generate a launch file. For example, the session host mayhave a first IP address, but the session host may indicate analternative address that client devices should use to connect. Thesession host therefore identifies the specific desktop (or other hostedresource) by IP address or other address information usable by thesession client to connect to that hosted service. In addition, thesession host may take steps to prepare for the future incomingconnection, such as breaking one or more existing connections toresources on the session host and/or opening network ports ready toreceive a connection from a client device.

In step 611 lease presenter 604, using the information received fromsession host 606, generates a standard ICA/RDP launch file (based on theprotocol in use by the session client, e.g., which could also oralternatively include PCoIP, RGS by Hewlett-Packard, and the like), andsends the launch file to the session client. The lease presenter may usethe lease token to determine the parameters for a conventional launch,in combination with the additional information received from the sessionhost, thereby enabling backwards compatibility with session client(endpoint) devices that are unaware of connection leases. The sessionclient thus received from the lease presenter the same sort of fileexpected to be received in response to the session client's initialrequest to connection broker 401. The session client then uses thereceived launch file in step 613 to establish the session with thesession host and, more specifically, with the specific hosted services(desktop, application, etc.). Using the method of FIG. 6, an existinglegacy session client can establish a session using the lease tokenmethods and systems described herein. The session host can autonomouslydetermine the validity of the lease and whether to permit the sessionconnection, without communicating with the connection broker.

According to some aspects, the session host may be configured withsoftware to accept connection leases and respond as described herein.According to other aspects, a layer of abstraction may be added tosession hosts, similar to the layer of abstraction added to sessionclients discussed above. That is, where a session client is not alease-aware client, the lease presenter 604 acts as an intermediary onbehalf of the session client to help establish the connection based on alease token. Similarly, in some aspects a “lease receiver” may beconfigured to operate with session hosts that are not independentlylease-aware devices. Stated differently, in some aspects the sessionhost functionality may be separated from the component to which leasesare presented.

According to an alternative aspect, with reference to FIG. 7,lease-aware session clients may be deployed that include thefunctionality of the lease presenter 604 (FIG. 6). In this example, instep 701 lease-aware client 702 initially contacts connection broker401, as lease issuer, for a connection lease. In step 703 connectionbroker 401 generates the lease token and returns the lease token tolease-aware client 702. Connection broker may also store a copy of thelease token in one or more other redundant lease stores (not shown).

In step 705 lease aware client 702 presents the lease token, along withany required authorization credentials, to session host 704. Sessionhost 704 validates/authenticates the token, and provides any additionalinformation to client 702 that may be needed to establish the connectionbetween client 702 and a specific resource identified in the leasetoken, e.g., a specific desktop, application, etc. Client 702 thenestablishes the session based on the additional information receivedfrom the session host 704.

While the methods of FIG. 6 and FIG. 7 depict two illustrative examples,other variations may be made without departing from the spirit or scopeof advances described herein. For example, a lease token (or a separatelease) may include information to authorize a network connection througha security device, such as an access gateway, in which case the leasemay be presented to the gateway as part of establishing the connectionwith the session host. In addition, cryptographically signed lease tokenpresented to the security device may include the host (or hosts) andnetwork ports to which the lease presenter is permitted access, so thegateway may restrict network access to just those hosts.

In another aspect, the connection lease (or a separate lease) mayinclude the address (or addresses) of services that can boot sessionhosts, so that that if the required session hosts are powered off, uponpresentation of an appropriate lease the lease presenter may requestspecific session hosts to be booted. In this case, the lease may includea hardware and/or VM identifier for session hosts.

In yet other aspects, some information in the connection lease may beencrypted to prevent information disclosure to less-trusted components,such as client (endpoint) devices. In such an example, some informationmay remain unencrypted, e.g., information about the validity period ofthe lease (if any), and the nature and addresses of any services towhich the lease may be presented (gateway devices, boot services orsession hosts), so that the lease presenter can determine whether thelease token is suitable for its purposes or not.

Lease issuance and renewal. Leases may be issued a-priori, or on demand.As an administrator determines who is permitted to connect to whichresources, the Lease Issuer may pro-actively create leases and placethem in the lease store without waiting for a specific connectionrequest from a session client. Alternatively, leases may be issued as auser requests a connection to a particular resource, or the first timethat a user requests a connection to a particular session host.

Similarly, leases may be renewed (by being re-issued) pro-actively oron-demand. To ensure continuous availability, leases may be renewedbefore they expire. The renewal may be initiated by the lease issueracting autonomously, or by the lease presenter determining that a newrenewed lease is desirable. The lease issuer may include information inthe lease, for the benefit of the lease presenter, indicating when thelease should be renewed.

Lease revocation. Once a lease is issued in the form of a lease token,it is possible that the lease should be revoked before the leaseexpires. That is, leases may need to be revoked when an administratorremoves a user's access to a session host (or application). A lease mayalso need to be revoked based on deprovisioning a user from the overallsystem (such as for terminated employees), or when a session host isdeprovisioned or taken offline. Leases may also need to be revoked basedon policy considerations, such as when users only need to have access toa session host for limited period of time, or based on user behaviorwhere a lease would be revoked after a certain period of inactivity.

Leases may be revoked in various ways. Where a user or session host isdeprovisioned, the lease simply will not work because one of therelevant connection endpoints no longer exists on the system. In anotherscenario, a lease may be revoked based on a unique identifier 523associated with each lease token. A list of revoked identifiers may bedistributed to appropriate session hosts (those identified in thelease), so session hosts can autonomously decline revoked leases if orwhen presented to that session host. Alternatively, a list of revokedidentifiers may be stored in a central location (at the lease store,lease issuer, etc.), and each session host queries the centralrepository using a lease's unique identifier, when presented, to confirmwhether the lease is valid or whether the lease has been revoked. Inanother example, a lease may be revoked based on the cryptographic keyused to sign the lease having been revoked. The cryptographic key may berevoked using standard technologies, such as X509 certificates andcertificate revocation lists (CRLs) used to manage cryptographic keyrevocation. Any of the above revocation methods may be used incombination, or separately, to control lease revocation.

Using one or more aspects described above, the use of connection leasesand lease tokens provides greater resilience by reducing the dependenceof virtualization systems on central infrastructure and single points offailure, and further provides the ability to scale up quickly and easilyfor managed hosted applications and desktops. The ability to scale upresults from a connection broker being queried less often per sessionclient. As a result a single connection broker has the ability toservice a much larger number of session clients when using connectionleases and lease tokens as described herein, as opposed to prior artinline connection broker architectures.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asillustrative forms of implementing the claims.

What is claimed is:
 1. A session host apparatus, comprising: a processorcontrolling operations of the session host apparatus; and memory storingcomputer readable instructions that, when executed by the processor,cause the session host apparatus to establish a session with a sessionclient by: providing, to the session client and based on a resourceassignment of a connection broker apparatus, one or more resourceshosted by the session host apparatus; receiving a lease token associatedwith the session client, wherein the lease token is a self-sustainingpackage of cryptographically signed connection lease data from which thesession host apparatus can determine, regardless of an outage of theconnection broker apparatus, whether the session client is authorized toaccess one or more resources hosted by the session host apparatus, thelease token configured based on one or more resources previouslyassigned to the session client by the connection broker apparatus;determining, based on the lease token, one or more resources, hosted bythe session host apparatus, that the session client is authorized toaccess; sending connection information to the session client based onthe one or more determined resources, after determining that the sessionclient is authorized to access the one or more resources hosted by thesession host apparatus; and establishing a session with the sessionclient to provide access to the one or more determined resources.
 2. Thesession host apparatus of claim 1, wherein determining compriseschecking a lease token revocation database to determine whether thelease token has been revoked.
 3. The session host apparatus of claim 1,wherein the lease token comprises a plurality of data fields, each datafield defining a different one of: a lease ID; a set of one or moreclients; a set of one or more session hosts; and a set of one or moreresources.
 4. The session host apparatus of claim 3, wherein the leasetoken is signed by the connection broker apparatus.
 5. The session hostapparatus of claim 3, wherein the lease token comprises a plurality ofsecurity policy data fields, each security policy data field defining adifferent one of: a set of one or more access conditions; a connectionlimit; a maximum idle time; and a maximum disconnect time.
 6. Thesession host apparatus of claim 5, wherein the access conditions dependon a state of anti-malware software on the session client.
 7. Aconnection broker apparatus, comprising: a processor controllingoperations of the connection broker apparatus; and memory storingcomputer readable instructions that, when executed by the processor,cause the connection broker apparatus to administer a connection leaseby: receiving a connection request from a session client; based on thesession client, determining: one or more session hosts the sessionclient is authorized to establish a session with, and one or moreresources the session client is authorized to access on said one or moresession hosts; assigning the one or more determined resources to thesession client; generating, based on one or more resources previouslyassigned to the session client by the connection broker apparatus, alease token as a self-sustaining package of cryptographically signedconnection lease data from which each of the one or more session hostscan determine, regardless of an outage of the connection brokerapparatus, whether the session client is authorized to access one ormore resources hosted by that session host, the self-sustaining packagehaving a first data field identifying a lease number, a second datafield identifying the one or more session hosts, a third data fieldidentifying one or more resources the session client is authorized toaccess, and a fourth data field identifying the session client;cryptographically signing the lease token to verify that the lease tokenoriginated at the connection broker apparatus; and sending the signedlease token to a lease store for storage.
 8. The connection brokerapparatus of claim 7, wherein sending the lease token includes sendingthe lease token to one or more of: the session client for storage on thesession client, and a central lease store accessible by the one or moreidentified session hosts.
 9. The connection broker apparatus of claim 7,said instructions further causing the connection broker apparatus toperform: receiving a request to revoke the lease token; and revoking thelease token by publishing the lease number to a central revocation list.10. The connection broker apparatus of claim 7, said instructionsfurther causing the connection broker apparatus to perform: receiving arequest to revoke the lease token; and revoking the lease token bysending a revocation message to each of the one or more session hostsidentified in the lease token.
 11. The connection broker apparatus ofclaim 7, said instructions further causing the connection brokerapparatus to perform: receiving a request to revoke the lease token; andrevoking the lease token by revoking a cryptographic key used to signthe lease token.
 12. The connection broker apparatus of claim 7, whereinthe lease token further includes a fifth data field identifying a set ofone or more access conditions, a sixth data field identifying aconnection limit, a seventh data field identifying a maximum idle time,and an eighth data field identifying a maximum disconnect time, whereineach of the fifth through eighth data fields are usable by a sessionhost identified in the second data field to implement a security policy.13. The connection broker apparatus of claim 7, said instructionsfurther causing the connection broker apparatus to perform: receiving,after the lease token is expired or revoked, a subsequent connectionrequest from the session client; and assigning, based on the subsequentconnection request, one or more resources to the session client.
 14. Amethod comprising: providing, to a session client and based on aresource assignment of a connection broker apparatus, one or moreresources hosted by a session host apparatus; receiving, by the sessionhost apparatus, a lease token associated with the session client,wherein the lease token is a self-sustaining package ofcryptographically signed connection lease data from which the sessionhost apparatus can determine, regardless of an outage of the connectionbroker apparatus, whether the session client is authorized to access oneor more resources hosted by the session host apparatus, the lease tokenconfigured based on one or more resources previously assigned to thesession client by the connection broker apparatus; determining, based onthe lease token, one or more resources, hosted by the session hostapparatus, that the session client is authorized to access; sendingconnection information to the session client based on the one or moredetermined resources, after determining that the session client isauthorized to access the one or more resources hosted by the sessionhost apparatus; and establishing a session with the session client toprovide access to the one or more determined resources.
 15. The methodof claim 14, wherein the lease token comprises: a first data fieldidentifying a lease number corresponding to the lease token; a seconddata field identifying one or more session hosts; a third data fieldidentifying one or more resources; and a fourth data field identifyingone or more session clients permitted to access the one or moreresources hosted by the one or more session hosts.
 16. The method ofclaim 15, wherein each resource is one of a hosted desktop and a hostedapplication.
 17. The method of claim 15, wherein the lease token furthercomprises: a fifth data field identifying a set of one or more accessconditions that must be met by the one or more session clients in orderto access the one or more session hosts; a sixth data field identifyinga connection limit; a seventh data field identifying a maximum idletime; and an eighth data field identifying a maximum disconnect time,wherein each of the fifth through eighth data fields are usable by asession host identified in the second data field to implement a securitypolicy.
 18. The method of claim 17, wherein the connection limit isusable to constrain when the one or more session clients can access theone or more session hosts.
 19. The method of claim 15, wherein the leasetoken further comprises a fifth data field identifying virtual channelinformation usable by the one or more session hosts to allow or denyaccess by the one or more session clients to one or more virtualchannels on the one or more session hosts.
 20. The method of claim 15,wherein the lease token further comprises a fifth data field storing asignature usable by the one or more session hosts to verify that datastructure of the lease token is unaltered, and that the lease tokenoriginated from the connection broker apparatus.